The invention relates to a frictionally engaged driving belt having a base body and a cover layer comprised of rubber or a rubber-like synthetic material (i.e. an elastomeric synthetic material) which is provided with a load-carrying or tractive support layer that is embedded into the rubber or the rubber-like synthetic material.
In connection with frictionally engaged driving belts or force transmission belts such as, for example, flat belts, V- or wedge belts, and poly-V- or wedge rib belts, these are commonly deployed in situations in which a large transmission ratio must be realized and a high demand is placed on the belt in view of the expected wear resistance, noise handling capability, and dynamic load capacity. Thus, driving belts are deployed, for example, for force transmission in application areas ranging from office machines up to the heaviest machine drives. Driving belts are deployed in manifold configurations as well with respect to vehicles and, indeed, especially in those circumstances concerning a de-coupling of the oscillations of the drive assemblies and the associated driven assemblies. V-belts are, for example, deployed in vehicles for the driving of electrical generators (alternators). Ribbed V-belts offer the advantage that they combine the high flexibility of flat belts with the efficient power transmission of V-belts and also can be deployed in complex drive constructions involving bending of the belt during reverse belt travel effected via change of direction rollers and moving idlers.
In drive elements, the outer surfaces of the belt are subjected to various weather and operational medium influences. In spite of these influences, the belt should exhibit a long operational life and, at the same time, in particular in the areas of vehicle and domestic product industry applications, the running noise should be minimized. Noises occur due to drive elements which act to create frictional traction for effecting the transmission of force by the belt and frequently, if, for example, during wet, cold weather, certain friction behaviors occur between the belt surface and the drive disc or pulley, squeaking tones emanating from oscillations or vibration will occur. These noises can be minimized or damped via various measures.
Different approaches have been proposed to minimize the noise development ensuing from frictionally engaged driving belts depending upon the respective manufacturing process for manufacturing the driving belt. If one, for example, takes note of such approaches from the perspective of the manufacturing processes for ribbed V-belts, in connection with which substantially two manufacturing processes, the cutting process and the molding process, have come to the fore, it is known to mix in fibers into the rubber mixture formulated for the ribs to reduce the development of noise from the belt via travel over the belt disk.
The cutting process for belts with fiber-containing mixtures is known, for example, via the disclosure in EP 642 886 A1. In connection with cutting processes, belt layers are produced and vulcanized which have a flat outer surface. Thereafter, the ribs are cut into the vulcanized belt surface. Via the calendering process during the production of the mixing plate for the belts, the mixture is provided with the fibers, which are preferably oriented transversely to the belt running direction. In the cutting process, the ribs are then cut out of the material such that the tips of the fibers extend outwardly out of the mixture surface. For the mixing in of such fibers in rubber mixtures, fiber materials such as cotton, polyester, polyamide such as, for example, nylon, and aramid are used. The favorable noise handling behaviors of such belts frequently do not remain over the entire operational life of the belt as the ribbed surface is eventually frictionly abraded to a smooth surface via passage over the disks and there remains no more of the outwardly projecting fibers which promote favorable friction conditions and a reduction of noise.
In a cutting process, a large portion of the often very expensive fiber reinforced mixture is thrown away as cutting waste. The alternative to the cutting processes is the ecologically and economically progressive molding process for the manufacture of ribbed V-belts which is, at the same time, more precise than the cutting process. In this connection, during the vulcanization process, the ribs are impressed into the substantially flat plate of an unvulcanized belt layer to project therefrom. In a molding process, as well, fibers can be mixed into the rubber mixture which forms the rib and can be vulcanized in therewith as is disclosed, for example, in U.S. Pat. No. 5,904,630. The fibers succeed thereby into locations in the interior of the ribs of the rib contour. Additionally, it is known from U.S. Pat. No. 5,904,630 to cut the ribs into the belt, still in a surface location, after the molding of the belt via the molding process in order to effect a working out of the fibers distributed within the mixture and thereby obtain a surface with fibers projecting therefrom. The durability of this noise reducing layer is comparable to that of a layer produced by the conventional cutting process.
Both the cutting and molding processes have in common that the frequently expensive fibers are present throughout the entire thickness of the rib rubber, although they are needed only on the surface. Moreover, the overall thickness of the fiber distribution is dictated by the desired characteristics of a belt mixture such as flexibility or workability and cannot therefore be increased arbitrarily to a more desirable value. Typical values for the portion of fibers in a belt mixture lie between 2 to 30 percent by weight of fibers per 100 percent by weight of total elastomer. It is more effective, in contrast, to place the fibers only at locations at which they are also required—namely, on the rib surfaces. Belts have heretofore been manufactured wherein the rubber mixture plate for the ribs has been provided with a securement layer on which thereafter short fibers have been distributed in a layering process as is disclosed, for example, in U.S. Pat. No. 3,190,137. The fibers produce, due to the concentrated application thereof in a thin layer, an effective noise reduction and, at the same time, produce, in most instances, an improvement in wear or abrasion. Typically, it is common in such layers to use short cotton fibers which exhibit a good compromise between cost and noise reduction. Wool is not suitable for the thermal demands which are imposed on the material. In connection with synthetic fibers such as aliphatic polyester, for example, based on polyethylene terephtalate or polyethylene napthenate, polyamide 6, or polyamide 6.6, no positive influence is found on the noise behavior so that deployment of these fibers does not make sense to achieve a noise reduction. The smooth surfaces of these synthetic fibers appear to be responsible for the fact that, evidently, no satisfactory positive influences on the friction behavior and dampening of noise are effected.
The present invention provides a solution to the challenge of providing a frictionally engaged driving belt in which a noise development in the driving of the belt is minimized or prevented.